The present invention relates to a system for providing automatic margin alignment for digital document processors. The invention is particularly suitable for use with systems where a user creates a document using a high level language, such as a page description language, then rasterizes the image to provide raster image data, for example, for printing at a laser printer.
During document processing, computer generated images are rasterized and recorded on, e.g., laser printers, color or monochrome copiers, or used to expose frames of photographic film or the like.
To obtain the computer generated images, a user first generates a graphic image file using a computer graphics program, also referred to as a graphics application or a graphics layout program or software. The graphic image file may include one or more images or frames of image data which, for example, are in a bit mapped or text (e.g., ASCII) format. The image data are processed by a raster image processor (RIP), which provides frames of raster image data for use by an output device in generating images. Commonly available output devices include a graphic display monitor, film recorder, laser printer or copier.
Digital document processing systems have become increasingly popular since they allow a user to prepare relatively sophisticated, high quality documents, such as brochures, pamphlets, and the like. Moreover, such systems are relatively inexpensive and are therefore accessible for personal use or small business use.
Typically, the graphics layout software is run on a personal computer or a work station. The computer may be a stand alone unit or part of a network. The computer has an input device, such as a keyboard or a mouse, and a video display monitor that allows the user to preview an image before it is printed. The computer is typically interfaced to a printer for outputting data via a graphic image server, and to a scanner for receiving image data. The user assembles an image to be printed using a high level language such as a page description language wherein various graphical elements, e.g., logos, may be positioned in the image. The image elements may be positioned precisely within the image according to an on-screen measurement ruler or similar guide.
For example, it may be desired to insert a logo in the image at a specific distance from the top and sides of a page. Once the image is ready to be printed, it is provided to the graphic image server to be rasterized. The raster image data, which defines an image in terms of pixels, is then sent to the output device.
The graphic image server may comprise the EDOX.TM. system, for example, available from Management Graphics, Inc., Minneapolis, Minn., U.S.A., which includes a PC running Windows NT.TM.. Documents are created using a graphics layout software package, such as PhotoShop.TM. or Quark Express.TM., running on a client PC or Macintosh.TM. computer, and sent to the EDOX system. The EDOX system takes data, such as PostScript.TM. data, generated by the graphics layout software, and creates a corresponding raster image, which is then sent to an output device. The graphics layout software allows the user to lay out graphics and text on a page so that they are printed in a specific location on the page. For example, it may be required for the text margins to be one inch from the left and right edges of the page, and for the company logo to appear centered on the page.
However, oftentimes the image that is viewed by the user using the graphic layout software on a computer monitor is not exactly the same as the printed image. For example, variations among printers of different manufacturers, such as the paper feed mechanism, as well as variations in printers by the same manufacturer can result in mis-calibrations (e.g., mis-alignment) of a printed image on a page, i.e., wherein the printed image does not appear in the desired position on the page.
Various solutions have been proposed to address this problem. For example, one approach requires the user to print a calibration page and to measure the mis-calibration using a ruler. Then, the user modifies the graphics layout software or graphic image server software by manually inputting the mis-calibration distances, e.g., as (x, y) coordinates. Another approach requires the user to print a duplexed (two sided) calibration page. The user then holds the page up to a light to determine a set of lines on each side which line up correctly. The user then manually inputs the appropriate information to the software. However, these approaches are generally unsatisfactory because they rely on the user to determine the degree of mis-calibration. The user may make a measurement error, may make an error in inputting the calibration information to the software, or may otherwise not follow the required instructions.
One proposed calibration solution calibrates a scanner, then calibrates a printer. A pre-printed, known test image that is printed based on pre-stored test image data in the computer. The printed image is then scanned in, and the computer compares the scanned-in image with the pre-stored image data using an image comparison algorithm to calibrate the system. The system essentially locates which pixels on the scanned-in image and the pre-stored image correspond to one another and provides an appropriate translation value, e.g., using a raster-to-raster transformation. Sufficient memory space is therefore required to store the two images.
Moreover, the need for sophisticated image comparison software raises the complexity and cost of the system. Also, it is inconvenient for the user to locate the pre-printed, known test image before a calibration can be performed since the pre-printed image is just a sheet of paper that can easily be misplaced. Additionally, mis-calibrations can still remain since the system calibrates a print out to pre-stored data, but does not calibrate the print out to the image viewed on a monitor by the user using the graphics layout software. That is, the image seen by the user is not calibrated-to the printed image since the calibration is not applied during rasterization of the image data from a graphics layout software. Moreover, the need to calibrate both the scanner and the printer introduces additional complexity.
Accordingly, it would be desirable to provide a method and apparatus for calibrating a printed or otherwise imaged document to an image in a document processing system. The system should provide calibration of the horizontal and vertical margins of a printed document. The system should be compatible for use with printers and other imaging devices made by different manufacturers.
Furthermore, the system should be relatively easy to implement by the user, and not require the input of any calibration data by the user. The system should not require calibration of a scanner. The system should be compatible with existing graphics layout software tool. The system should be implementable in a graphics image server during rasterization of image data.
The present invention provides a system having the above and other advantages.